The most prominent organ of larval mosquitoes is the stomach, which makes up the major part of the gastrointestinal tract. This organ is of prominent importance for ionic, volume and acid/base homeostasis. The anterior stomach actively secretes alkali equivalents, generating a compartment of extremely high pH which is of importance for digestion, but also for the susceptibility to biological control agents such as Bacillus thuringienis endotoxin. In the posterior stomach the pH returns to almost neutral values by recovery of alkali equivalents. Most likely, this cycle involves a high turnover of acid/base equivalents as well as of sodium and chloride ions. The processes of ion transport, their regulation and their coordination with peristalsis in the stomach of larval mosquitoes are poorly understood. The project is directed at understanding these processes in two mosquito species: the yellow fever mosquito (Aedes aegypti) and the malaria mosquito of subsaharan Africa Anopheles gambiae. Specifically we will determine: 1. the ion transport mechanisms involved in alkalization of the anterior stomach. 2. the ion transport mechanisms involved in reacidification of the posterior stomach. 3. the mechanisms of regulation of ion transport in the anterior and posterior stomach. 4. the mechanisms of coordination of ion transport with peristalsis in the anterior and posterior stomach. The studies will be carried out, using mainly five different methodological approaches: 1.) Electrophysiological characterization of ion transport across isolated stomach segments and its regulation, using conventional transepithelial techniques and microelectrodes 2.) Analyses of luminal pH changes with isolated stomach segments, using pH indicators and/or pH sensitive microelectrodes in the perfusate 3.) Histochemical and immunhistochemical localization of involved transporters and regulative units/systems 4.) Biochemical determination of transporter activities and their regulation by hormonal/non-hormonal factors 5.) Analyses of peristalsis and its regulation with electrophysiological techniques and image analyses. The results of this project will provide information about specific targets for the development of mosquito control agents.